Various types of rolling doors have long been used, particularly in regard to commercial and industrial buildings. Basically, rolling doors consist of a curtain of articulated slats which can be raised and lowered to selectively open and close a doorway or other opening in a building. The curtain is rolled and unrolled from some type of roll cylinder which is mounted horizontally adjacent the top of the doorway. This is a major advantage of rolling doors in that the door does not extend inwardly into the building from the doorway, as is the case with overhead doors which have a plurality of articulated panels which require tracks extending into a building for storing a door when it is in the open position. Of course, this characteristic of overhead doors restricts utilization of overhead space in a building having an overhead door in the area occupied by the tracks for the door panels.
Rolling doors conventionally have compensating systems to counterbalance the weight of the articulated curtain and any attachments thereto. Such counterbalancing systems normally employ a torsion spring or other biasing element which may be mounted within the roll cylinder. The roll cylinder is normally mounted on a drive shaft which may be powered by a drive system consisting of a motor and gear reducer coupled by a drive chain to a sprocket nonrotatably mounted relative to the drive shaft.
A potential for damage to the system or injury to operating personnel exists in the event of failure of certain components of rolling door systems. For example, in the event of a broken counterbalance spring, a broken roller chain, or a power failure or reduction of voltage to the electric motor, the door may be released in such a fashion that it undergoes a free fall. As rolling doors are frequently constructed of relatively heavy materials, there is the possibility of extensive damage to the door slats or other system components, not to mention damage to property or persons located in or proximate to the door opening at the time of such a free fall.
Since the possibility of component or power failures and the resultant free fall consequences have been appreciated in the industry for some time, efforts have been made to develop different types of stop mechanisms for rolling doors. In many instances, the existing stop mechanisms tend to be over sophisticated, variable in operation, or have other disadvantageous operation or maintenance characteristics.
One type of device which has appeared in the industry employs cammed sprags that are pushed away from their housing by the power input mechanism of the stop device. Rotation from the output side of such stop mechanisms, as by a spring imbalance or failure, is prevented by the sprags locking against the housing. In some instances, stop mechanisms of this type can experience problems with repeat locking and unlocking and thus, provide erratic operation due to spring imbalance or other minor intermittent variations in resistance provided by movement of the door. In addition, stop mechanisms of this type may have highly critical tolerances and may require that support bearings be used at both ends to insure that no bending is introduced via the shaft to avoid lockups being artificially triggered.
Another type of device which is used as a stop mechanism for rolling doors employs roller or ball bearings which are positioned in pockets in the centrally disposed rotor during normal operation. When excessive angular velocity of the rotor attached to the drive shaft takes place, the ball bearings are thrown outwardly into recesses formed in the stationary ring surrounding the rotor with the configuration of the ring and the slots for the balls being arranged in such a manner as to trap or jam the ball bearings between the rotor and the stationary ring to thereby effect stopping and locking of the stop mechanism. Stop mechanisms of this type may exhibit a lack of uniformity with respect to the extent of rotation which takes place before jamming or locking may occur. Another problem with stop mechanisms of this type is that component replacement or factory servicing may be necessary or desirable after each actuation of the locking mechanism. Besides the operational disadvantages noted above and the potential for frequent service, the existing devices tend to be expensive and frequently not sufficiently rugged to withstand the use and abuse to which such stop mechanisms and rolling doors are routinely submitted.